This application claims priority of Taiwanese application no. 92202847, filed on Feb. 24, 2003.
1. Field of the Invention
The invention relates to a power tool, more particularly to a power tool having an operating knob for controlling operation in one of rotary drive and hammering modes.
2. Description of the Related Art
A conventional power tool according to U.S. Pat. No. 6,202,759 includes a fixing gear wheel, an output axle, a spring, a movable gear wheel, a switching member, a fixing ring, a housing, and a rotary collar.
The fixing gear wheel is disposed immovably in the housing and is formed with first ratchet teeth. The output axle extends rotatably through the fixing gear wheel and is axially movable between front and rear limit positions relative to the fixing gear wheel. The spring serves to bias the output axle to the front limit position. The movable gear wheel is mounted on the output axle for co-rotation therewith and is formed with second ratchet teeth that confront the first ratchet teeth of the fixing gear wheel. The second ratchet teeth disengage the first ratchet teeth when the output axle is at the front limit position, and engage the first ratchet teeth when the output axle is at the rear limit position. The switching member has the output axle extending rotatably therethrough, is coupled to and is movable together with the output axle between the front and rear limit positions, and has a periphery formed with peripheral latching projections. The fixing ring is disposed between the switching member and the movable gear wheel, and is formed with a through hole that permits extension of the output axle therethrough. The through hole is defined by a periphery that is formed with retaining notches corresponding to the peripheral latching projections on the switching member. The housing is disposed to surround the output axle so as to confine the fixing gear wheel and the movable gear wheel therein. The rotary collar is sleeved rotatably on the housing, and has an inner wall formed with grooves corresponding to the peripheral latching projections of the switching member. As such, when the rotary collar is rotated, the switching member rotates accordingly so as to align or misalign the peripheral latching projections of the switching member and the retaining notches of the fixing ring, thereby enabling or disabling movement of the output axle between the front and rear limit positions for operating the power tool in one of rotary and hammering modes.
It is desirable to provide a power tool of the aforesaid type that has an operating knob requiring minimum force to switch between the rotary drive and hammering modes, that can ensure smooth and stable operation of a drive spindle, and that has components which are relatively easy to assemble.
According to the present invention, a power tool comprises a motor assembly, a fixed ratchet seat, a drive spindle, a biasing member, a rotatable ratchet, a latching seat, a switching ring, a torsion spring, a generally cylindrical housing, and an operating knob. The motor assembly has an end cap. The fixed ratchet seat is disposed externally of the motor assembly, is disposed non-movably and adjacent to the end cap, and is formed with first ratchet teeth. The drive spindle extends rotatably through the fixed ratchet seat and further extends rotatably and slidably through the end cap. The drive spindle is coupled to and is driven rotatably by the motor assembly. The drive spindle is axially movable between front and rear limit positions relative to the end cap. The biasing member serves to bias the drive spindle to the front limit position. The rotatable ratchet is mounted on the drive spindle for co-rotation therewith, and is formed with second ratchet teeth. The second ratchet teeth disengage the first ratchet teeth when the drive spindle is at the front limit position. The second ratchet teeth engage the first ratchet teeth when the drive spindle is at the rear limit position. The latching seat has the drive spindle extending rotatably therethrough. The latching seat is coupled to and moves together with the drive spindle between the front and rear limit positions. The latching seat has one end adjacent to the rotatable ratchet and formed with at least a peripheral latching projection. The switching ring is disposed between the latching seat and the rotatable ratchet, and is formed with a through hole for extension of the drive spindle therethrough. The through hole is defined by a periphery that is formed with at least a retaining notch corresponding to the peripheral latching projection on the latching seat. The switching ring is rotatable relative to the drive spindle from a first angular position, where the peripheral latching projection is misaligned from the corresponding retaining notch and abuts against the periphery of the through hole in the switching ring such that movement of the drive spindle from the front limit position to the rear limit position is prevented, to a second angular position, where the peripheral latching projection is aligned with the corresponding retaining notch so that when the drive spindle is forced toward the end cap of the motor assembly for moving from the front limit position to the rear limit position against the biasing action of the biasing member, the latching projection moves into the corresponding retaining notch. The switching ring is formed with an operating arm extension parallel to and offset from the drive spindle. The torsion spring is connected between the latching seat and the switching ring for biasing the switching ring from the second angular position to the first angular position. The housing is mounted on the end cap of the motor assembly and is disposed to surround the drive spindle so as to confine the fixed ratchet seat, the rotatable ratchet, the latching seat and the switching ring therein. The housing permits the operating arm extension to extend outwardly therefrom. The operating knob is sleeved rotatably on the housing, and has an inner knob surface formed with a pushing unit. The operating knob is rotatable relative to the housing in a first direction to cause the pushing unit to engage the operating arm extension for moving the switching ring from the first angular position to the second angular position against biasing action of the torsion spring, and in an opposite second direction that enables the torsion spring to provide a restoring force for restoring the switching ring from the second angular position back to the first angular position.